The invention relates to a method of reducing voltage surges linked to the operation of a current breaking device in a high-voltage electricity network by determining optimum switching times for that device.
In the prior art, such control devices are designed to monitor the operating status of current breaking devices and to send early warnings, which is the best way to prevent network faults and to extend the service life of the device.
Prior art control devices incorporate new functions that render them “intelligent” through diagnosing not only the state of the parameters specific to the current breaking device but also the parameters of the network. They can thus issue local instructions to open or to close the electrical devices that they monitor.
Thus, as described in reference document [1] (see list at the end of the description), a plurality of circuit-breaker parameters are taken into consideration:                stored energy (pressure, spring load, etc.);        control voltages;        arc extinction medium state and characteristics;        ambient temperature;        number of previous actuations;        ageing effects;        periods between actuations.        
The influence of these parameters on the actuation time is strongly linked to the design of the circuit-breaker and must be evaluated for each application.
A plurality of network parameters can also be monitored to provide the control device with sufficient intelligence. Usually, the voltage on the supply side of the breaking device must be monitored. Sometimes the voltage on the load side of the breaking device and the current flowing through it must be monitored.
It must be remembered that the operation of high-voltage circuit-breakers, in particular line circuit-breakers, causes high transient inrush currents and voltage surges that make it obligatory to overspecify the electricity transport infrastructures: pylon dimensions, surge arrester size, etc. These voltage surges and inrush currents are an important constraining factor for high-voltage equipment, in particular transformers. Operating such a circuit-breaker at the optimum time relative to the voltage conditions existing at its terminals reduces these voltage surges and/or inrush currents. However, such a circuit-breaker has a long actuation time, i.e. the time between the time at which the close instruction is issued and the time at which the main contacts close, for example 50 milliseconds (ms). Although predicting an optimum actuation time is easy with purely sinusoidal signals (reactances, transformer's, capacitor banks), it is much less so in a “transmission line” application where the waveforms are complex and highly variable.
The field of application of the present invention is thus that of synchronous closing, otherwise known as point on wave (POW) switching, of high-voltage circuit-breakers enabling precise and reliable prediction of the optimum actuation times to limit oscillation phenomena on the high-voltage network liable to cause high voltage surges and to damage the electrical equipment, taking into account the problem of compensated or uncompensated lines.
The prior art devices include insertion resistances, as described in reference document [2]. These lead to a high overhead, however.
The object of the invention is to provide a method using a new control law to improve the prediction of the ideal time to close electrical current breaking devices in a high-voltage network.